Mineral filtering substance



Patented Sept; 17, 1935 Perley G. mach, Washington, D. c.

No Drawing. Application August 31, 1934, Serial No. 742,353

'lClaims.

This invention relates to a method of revivifying or activating mineral substances for use as filtering agents and of re-activating spent mineral filtering agents, and is particularly useful in 5 restoring agents used as filtering, bleaching, de colorizing and deodorizing media for oils,v fats, waxes, gums, fruit juices, sugars and the like to the original degree of activation.

The invention always comprehends the prodl ucts resulting from treating a mineral filtering agent in the manner hereinafter described, inasmuch as my process is eifective in many instances to revivifya spent agent to more than its original degree of activation.

This application is a continuation in part of my original application Serial No. 526,543 dated March 30, 1931, and entitled Mineral filteringsubstances. In said original application I described'several novel methods of preparing desirable mineral filtering substances from both natural and synthetic materials, all-of said methods having been developed as the result of extensive experiments which led to the discovery that filters of this classfunction through forces 25 of selective adsorption existing between the darker and more active (usually basic) constituents of a fluid to be filtered and the chemically active (usually acid) surfaces of the filter material, the remaining fluid being thereby rendered less highlycolored and chemically more stable. The filtering power of a selectively adsorbing filtering material thus apparently resides in the chemical condition of the filter surface and accordingly my 3 invention in its broadest aspect residesdn the on natural or prepared minerals, which substancesare thereby rendered selectively adsorbing with respect to fluids of the character above indicated. i

The experiments which have led to the discovery fo'rmingthe subject-matter of the present invention included a careful study of both natural and synthetic mineral filters as previously known, such as for example the (natural) fullproduction of suitable chemically active surfaces 7 ers earths and bentoni'tes and (synthetic) silica terized by what I choose to designate open bonds, which condition is evidenced by an inherent absorptive force which continues until existing external forces are balanced. In the presence .of a vapor, the active surfaceof the filter first adsorbs H and OH radicals over its surface from the vapor. This thin initial layer is in the form of a liquid film which increases in thickness until its vapor pressure approaches that of the surrounding vapor at which the existing forces are 10 in equilibrium. Similarly, in the presence of a solution the active surface of the filtering material adsorbs the substances (usually basic) in solution until the forces are balanced by the The theory underlying the creation or production of chemically active surfaces characterized by open bonds is well illustrated in the case of silica gel as prepared by combining solutions of water glass and acid. Silica gel as thus prepared is considered to: [be in the form of long chains of molecules. represented by (HaSiODnl'hO. From such chains (n+1)H2O radicals may be driven ofi'by heating to elevated temperatures, thus creating open or unsatisfied case of silica Before heating I Z, E. if V H-o-s|i-o-si -o-A -oiii-em.

e i i iii w 0-Ai0 i0-Ai-0+ leto. v 5 l (I) l n sure; sci (mm) be activated ions or;

volatilizable by heat or' other simple means. Innatural filters (fuller's, in that ,while its surfaces are fully reactivated earth and the like) such ions are already present.

' In the synthetic filters (such as silica gel) they are incident to the structure produced by'the chemical reaction. By my invention there is rendered available for use as selectively adsorbing filtering substances a large number of natural and synthetic mineral substances which have heretofore been considered incapable of functioning in this manner.

One of vthe methods I developed for preparing activated mineral filters and which is referred to in my original application, is applicable to a restricted class of natural minerals, namely those decomposed granite and gneiss and serpentines. Acid treatment of such materials results in the replacement of the superficial basic elements of these minerals by hydrogen and hydroxyl ions. This class of minerals I find to be readily activated when in pulverized form, by partial leaching with an ordinary acid such as nitric, hydrochloric or sulphuric followed by thorough washing and then drying, preferably at a temperature of substantially 200 C.

My experiments in connection with the production of selectively adsorbing filtering media by this method have'also resulted in the discovery of a novel means of revivifying or reactlvating spent natural mineral filters such as Floridin fullers earths and bentonites used in filtering mineral oils. I have found that such spent earth may be completely restored to better than its original condition by treating it with a solution of chromium trioxide (chromic acid).

The oxide of chromium used (ClOa) in' forming chromic acidis'extremely soluble in water while the other oxides (CrO, CrsO: and ClOs) are insoluble. The stronger solutions attack bydrocarbons (so called wet combustion) much more vigorously than those more dilute. For reactivating used clay I use a solution composed of about equal parts of water andoxide. On

' mixing such a solution with an equal volume of dry used vigorous action starts in about one minute'with generation of considerable heat as long as the reaction continues. If the reaction is so violent as to boil afiay water, a little cold water is added to restrain the reaction. To re-' move the last traces of hydrocarbon from the clay, the chromic'acid solutiou is leftion the clay at least ten hours or overnightin a warm place, preferably 40 to 70 C. Y

This treatment with chromic acid oxidizes the adsorbed tarry coating of hydrocarbon to 11:0 and CO1, leaving the surface, after washing and desiccating at temperatures approximating 150' to 350 C., perfectly clean and fully as active as inits original rawstatewhile the minutepora intheearthremainlfl'le yfilled. Suchrevivifiedearthisbetterthantheorlglnalrawearth its retention-of oilds much decreased. Restoring spent earth in this manner is thus very simi-- lar in principle to the activation of minerals containing inorganic bases, the difference being that in this case the adsorbed basic material is organic. m either case the basic ions are replaced by the H and H ions and these latter are removed bydesiccation, leaving Op n bonds.

' By actual test, spent mineral filtering materials which have been restored or revivified by the above described method have proven to be more efiicient filtering and decolorizing agents than originally. -I attribute this to the fact that my process has not only removed the tarry con- 15 stituents of 'the liquids being treated which are adsorbed by and adhere to the filtering agent, but the acid treatment followed by desiccation at high temperature has produced new active surfaces characterized by open bonds.

Having thus described my invention, what I claim as new is:

1. The process of producing an active filtering surface on spent earth comprising treating a used earth with an aqueous solution of chromic oxide followed by washing out the excess solution with water and desiccating at temperatures between 150 C. and 350 C.

' 2. The process of producing an active filtering surface on an earth having intimately mixed therewith organic basic material comprising oxidising the organic basic material by contacting the mixture with chromic acid, then washing the mixture with water and desiccating the earth at a temperature between 150 C. and 350 C. 5

3. Anv active filtering agent comprising a suitable earth characterined by having its pores filled with the adsorbed constituents from a previous filtering operation, and its exposedsurface activated by chromic acid. treatment followed by 40 desiccation at temperatures'between 150 C. and 350 C.

4. The process of producing an active min filtering'agent from an earth having organic constituents replaceable by H and OH ions comprising replacing said organic constituents with H and OH ions by treating said earth with chromic acid, washing the earth to free it of excess acid, and then drying the earth at temperatures between 150 C. and 350 C. I

5. In the process of revivifv ns spent filtering materials employed in decoloring oils, syrups and the like, the step of contacting such filtering materials with chromic acid.

6. In the process of revivifying spent filtering materials employed in decolorizing oils, syrups and the like, the step of contacting such filtering materials with an aqueous solution of chromic oxide.

7.Intheprocess ofrevivifying spentfilteringfl materials employed in decolorizing oils, syrups and the like, the step of contacting such filtering materials withan aqueous solution of chromic 

